The present invention generally relates to clutch assemblies, and more particularly, to a light weight clutch assembly having improved durability and performance.
Vehicle clutches operate to selectively disengage an engine from a driven shaft for starting the engine and stopping the vehicle while in gear, and changing gears while in motion. When engaged, the clutches connect the engine and driven shaft so they turn in unison. Conventional clutches include a cover assembly having a cover and an annular pressure plate connected to the cover for simultaneously rotating with the cover. The cover is attached to a flywheel so the cover and pressure plate are spaced from the flywheel. A driven shaft extends through the cover assembly and is connected to a friction disc positioned between the pressure plate and flywheel. When the clutch is disengaged, the flywheel rotates independently from the driven shaft. The friction disc is splined to the driven shaft so the disc rotates simultaneously with the shaft, but so the disc is able to slide axially on the shaft. Springs between the cover and pressure plate force the plate toward the flywheel, clamping the friction disc against the flywheel so the driven shaft turns with the flywheel. The clutch is disengaged by a mechanical linkage that pushes levers pivotally mounted between the cover and the pressure plate. As the levers are pushed, the pressure plate moves toward the cover to disengage the clutch.
In some centrifugal clutches, the levers are formed so their mass is axially offset from the pins that connect them to the cover and pressure plate. Centrifugal forces pivot the levers outward due the offset masses when the clutch is spinning to increase clamping force. The cover must endure substantial reaction forces applied by the levers and springs. Further, the reaction forces can deflect the cover relative to the flywheel, reducing overall efficiency of the clutch. Conventionally, the cover is made from stamped steel and configured to resist the bending forces. However, over time the cover can fail as a result of the reaction forces. Moreover, the large size and weight of the cover undesirably increases its inertia. Thus, there is a need for a clutch cover assembly comprising a light weight cover that is capable of withstanding operational loading.
Conventional light weight pressure plates are milled from aluminum. Lever supports for connecting the levers to the pressure plate are machined integrally with the plate. Over time, abutting edges of the cover abrade the supports. Further, the integral lever supports crack at their base and eventually fail due to cyclical bending loads. In addition, the aluminum pressure plates tend to warp due to thermal loading from adjacent heat shields. Accordingly, there is a need for a clutch cover assembly having a light weight pressure plate that is capable of enduring operational loading.